The present invention generally provides improved kits, systems, and methods for radiosurgical treatment of moving tissues in a patient body. Exemplary embodiments may deposit a sufficient radiation dose at a target region of a heart so as to treat an arrhythmia of the heart. Along with allowing treatment of tissues which move at a relatively rapid pace, embodiments of the invention may accommodate significant deformation or relative repositioning of regions of the heart without subjecting the patient to unnecessary long-term trauma or inconvenience, and without unnecessarily constraining the time available for radiosurgical treatment planning
Tumors and other targets in the head, spine, abdomen, and lungs have been successfully treated using radiosurgery. During radiosurgery, a series of beams of ionizing radiation are often directed from outside a patient so as to converge at a target region, with the radiation beams often comprising MeV X-ray beams fired from different positions and orientations. The beams can be directed through intermediate tissue toward the target tissue so as to alter the biology of a tumor. The beam trajectories help limit the radiation exposure to the intermediate and other collateral tissues, while the cumulative radiation dose at the target can treat the tumor. The CyberKnife™ radiosurgical system (Accuray Inc.) and the Trilogy™ radiosurgical system (Varian Medical Systems) are two known radiosurgical treatment systems.
Modern radiosurgical systems incorporate imaging into the treatment system so as to verify the position of the target tissue and adjust to minor patient movements. Some systems also have an ability to treat tissues that move during respiration, and this has significantly broadened the number of patients that can benefit from radiosurgery. Radiosurgical treatments of other tissues that undergo physiological movements have also been proposed, including the directing of radiation toward selected areas of the heart for treatment of atrial fibrillation and other arrhythmias.
During atrial fibrillation, the atria lose their organized pumping action. In a healthy sinus rhythm, the atria contract, the valves open, and blood fills the ventricles or lower chambers. The ventricles then contract to complete an organized cycle of each heart beat. Atrial fibrillation, in contrast, has been characterized as a storm of electrical energy that travels across the atria causing the upper chambers of the heart to quiver or fibrillate. During atrial fibrillation, the blood is not able to empty sufficiently from the atria into the ventricles with each heartbeat. By directing ionizing radiation toward the heart based on appropriate lesion patterns, the resulting scar tissue may prevent recirculating electrical signals and thereby diminish or eliminate the atrial fibrillation.
While the proposed radiosurgical treatments of atrial fibrillation and other arrhythmias offer benefits by significantly reducing trauma for heart patients, improvements to existing radiosurgical treatment techniques may be helpful to fully realize the potential of such therapies. For example, tumors which move during respiration or the like may be targeted by surgically implanting high-contrast marker structures adjacent the targeted tumor. The marker acts as a fiducial, with the system identifying the location of the fiducial intermittently using biplane X-ray imaging techniques. Detailed images (such as computed tomography or CT) images of the heart tissues with the implanted fiducials are then obtained, and the series of intersecting radiation beams are carefully planned out so as to ablate the cancerous tumor. Unfortunately, taking enough X-ray images to adequately track the more rapid cardiac tissue movements associated with the heart beat cycle may subject collateral tissues to excessive quantities of image acquisition radiation. In fact, rather than tracking the implanted fiducials, known radiosurgical systems may monitor movement of a light-emitting diode (LED) fiducial array mounted on the skin of the patient so as to determine breathing and other patient movements. Biplane X-ray may then be acquired at a significantly slower rate than respiration: by only intermittently checking and revising the breathing cycle tracking with the X-ray images, such systems may adequately track respiration movement without imposing excessive imaging radiation. A variety of alternatives have been proposed for treatment of tissues which move with respiration and/or heartbeat, and while these proposals may eventually be shown to be viable for use in an arrhythmia treatment system, none has yet found widespread use. In the meantime, reliance on implanted fiducial structures in or near the tissues of the heart may present significant and unforseen challenges to general acceptance of radiosurgical treatments of tumerous and/or non-tumerous diseases of the heart.
In light of the above, it would be desirable to provide improved devices, systems, and methods for treating moving tissues of a patient, particularly by directing radiation from outside the patient and into the target tissues of a heart. It would be particularly beneficial if these improvements were compatible with (and could be implemented by modification of) existing radiosurgical systems, ideally without significantly increasing the exposure of patients to incidental imaging radiation, without increasing the system costs so much as to make these treatments unavailable to many patients, without unnecessarily degrading the accuracy of the treatments, and/or without causing unnecessary collateral damage to the healthy tissues of the patient despite the relatively rapid movement of the target tissues during beating of the heart.